1. Technical Field
The present invention relates to peak detection of signal waveforms, and in particular to an improved peak detection system. Still more particularly, the present invention provides a circuit for producing an adaptive threshold value for use with a peak detection system.
2. Description of the Related Art
In retrieving data from a storage system, a read channel is typically utilized to convert the data into a digital format. In a magnetic tape system, data is sensed by a read head and transformed into an analog signal. The analog signal may be amplified and filtered. Next, the signal is sampled and converted into a digital signal by an analog to digital (A/D) converter. Next a peak detector is employed in a read channel to aid in detecting logical ones and zeros in the digital signal. A peak detector is a data detection system that recognizes logic ones and zeros by locating the peaks of a waveform. The peak detector interprets a peak as a logic one. A peak detector typically performs two tests to detect a peak. First, the peak detector locates peaks in the waveform by locating the zero crossing of the derivative of the waveform, since a peak is associated with a derivative value of zero. In addition to detecting zero crossings, the peak detector also compares the peak value to a threshold. For a peak to qualify as a logic one, the peak value of the waveform should be greater than a predetermined threshold value. The threshold value is designed to be a fraction of the peak, usually 50 percent of the peak.
Such a system, however, may miss peaks or interpret noise as a peak as a result of signal amplitude variations in the read channel. Sources of signal amplitude variations may occur in many ways. For example in a magnetic tape system, variations in signal amplitude may occur as a result of the magnetic tape lifting off the read head due to particles or artifacts located on the magnetic tape. Vibrations and other conditions also may cause the magnetic tape to lift off the read head.
Some peak detectors have circuits for providing an adjustable threshold value. However, these circuits use the output of a peak detector as feedback to set or adjust the threshold value.
Therefore, it would be desirable to have a method and system for providing an adaptive threshold value to reduce errors in peak detection which occur as a result of signal amplitude variations.